This invention relates generally to communication systems and more particularly to line drivers for use in such communication systems.
As is known, data may be communicated from one entity (e.g., end users computer, server, facsimile machine, et cetera) to another entity via a communication infrastructure. The communication infrastructure may include a public switch telephone network (PSTN), the Internet, wireless communication system, and/or a combination thereof. Such a communication infrastructure supports many data communication protocols, which prescribe the software and/or hardware for accurate transmission of data from one entity to another. Such data communication protocols include digital subscriber line (DSL), asymmetrical digital subscriber line (ADSL), universal asymmetrical digital subscriber line (UADSL or G.Lite), high-speed digital subscriber line (HDSL), symmetrical high-speed digital subscriber line (HDSL), asynchronous transfer mode (ATM), internet protocol (IP), et cetera.
The hardware aspect of each of the various data transmission protocols specifies a termination impedance. For example, the ADSL transmission protocol defines the line termination impedance to be 100 Ohms. As a further example, SHDSL transmission protocol defines the line termination impedance to be 135 Ohms. If a line driver is to be used in a dedicated system (e.g., used in an ADSL system or SHDSL system only) the line driver can be designed to have the appropriate termination impedance. If, however, a line driver is to be used in communication systems that support multiple data transmission protocols, the impedances comprising the line driver must be changed depending on the data transmission protocol being supported. Typically, the line driver will be implemented on an integrated circuit that is mounted on a printed circuit board along with resistors. One common approach for changing the impedance of the line driver is to change the resistor values on the printed circuit board.
Therefore, a need exists for a line driver that has variable termination impedance that can be used in a variety of data transmission protocols without having to vary components on a printed circuit board.